Buried-Gate Image Sensor Structure for Low Leakage Pixels
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Solution Overview
Problem
As image sensors are miniaturized, increased leakage current occurs due to impurity diffusion from the floating diffusion region, leading to degraded optical properties and reduced integration density.
Innovation Solution
Incorporating a barrier impurity region and contact barrier region with gettering atoms like carbon and germanium around the floating diffusion region to suppress impurity diffusion and a metal silicide intermediate layer to reduce contact resistance, thereby increasing the physical distance between the buried gate structure and the floating diffusion region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is reduced to increase integration density, then integration density is improved, but leakage current increases
Solution Approach 1:
The patent introduces a contact barrier region as a separate structural element between the contact and the floating diffusion region. This segmentation creates a distinct zone that prevents impurity diffusion while maintaining the electrical connection, allowing smaller pixel sizes without increasing leakage current.
Solution Approach 2:
The contact barrier region acts as an intermediary structure between the contact and the floating diffusion region. It includes a barrier impurity region with gettering atoms that mediate the interaction by suppressing impurity diffusion from the floating diffusion region into the contact, thereby reducing leakage current in miniaturized pixels.
2Ease of manufacture
If heat treatment process is performed after ion implantation, then manufacturing process is completed, but leakage current is generated due to impurity diffusion
Solution Approach 1:
The patent forms the contact barrier region with gettering atoms before the heat treatment process. This preliminary action ensures that when heat treatment is subsequently performed, the gettering atoms are already in position to suppress impurity diffusion, preventing leakage current generation while completing the manufacturing process.
Solution Approach 2:
The patent converts the potentially harmful effect of heat treatment-induced impurity diffusion into a beneficial outcome by introducing gettering atoms in the contact barrier region. These atoms actively capture and suppress diffusing impurities, transforming the harmful diffusion process into a controlled mechanism that reduces leakage current.
3Reliability
If contact resistance is decreased to prevent voltage drops, then electrical performance is improved, but physical distance between buried gate structure and floating diffusion region is reduced
Solution Approach 1:
The patent applies local quality by creating a contact barrier region with specific barrier impurity characteristics in the contact area, while maintaining the normal floating diffusion region properties elsewhere. This localized modification reduces contact resistance and prevents voltage drops without affecting the overall physical distance between the buried gate structure and floating diffusion region.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively reduces leakage current and maintains the optical properties of the image sensor, allowing for higher integration density and smaller pixel sizes without increased leakage.
Implementation Method 1
heat treatment processes following an ion implantation process during manufacture of an image sensor can generate a leakage current caused by outward migration or diffusion of impurities from a floating diffusion region
Implementation Method 2
A barrier impurity region including an impurity surrounding the floating diffusion region can suppress the leakage current, as the impurity includes atoms that serve as gettering atoms to suppress or prevent impurity atoms included in the floating diffusion region from diffusing outwardly
Implementation Method 3
disposing a contact pad and an intermediate layer on a contact within the image sensor increases a physical distance between a buried gate structure and the floating diffusion region and decreases a contact resistance
Data Source
AI summary
An image sensor may include; a semiconductor substrate including a first surface and a second surface, and further including a photoelectric conversion region, a buried gate structure disposed in a buried gate trench extending into the semiconductor substrate from the first surface of the semiconductor substrate, a floating diffusion region disposed on one side of the buried gate structure in the semiconductor substrate, a contact pad disposed on the first surface of the semiconductor substrate above the floating diffusion region and including polysilicon, an intermediate layer disposed on the contact pad and including a metal silicide, and a contact disposed on the intermediate layer and extending in a vertical direction perpendicular to the first surface of the semiconductor substrate.